The study of the activation and immune interactions of developing and mature T lymphocytes has been a major concern of our laboratory. This project proposes to identify T cell surface structures that are important for these funcitons through the development of monoclonal antibodies. These antibodies will be used in conjunction with both normal and transformed (hybridomas and lymphomas), T cell clones and heterogeneous cell populations. Preliminary studies have identified a novel, functionally important epitope on the surface of murine T lymphocytes. This project will develop monoclonal antibodies to novel T cell surface determinants and address the following aspects of these molecules: 1). The functional role of these molecules in cellular immune interactions and T lymphocyte activation. 2). The phenotypic and functional heterogeneity of normal and malignant T cells. 3). The expression and functional role of these determinants during T cell development. 4). The genetics and biochemical structure of these molecules.